Liquid level monitoring probes are utilized today as in-tank monitors for leak detection purposes. By monitoring such leakage, tank operators can reduce financial losses due to lost product and minimize impact on the adjacent environment. Such probe installations provide remote monitoring of changes in the level of product stored within a storage tank. Accurate monitoring of liquid level changes within underground liquid storage tanks is being increasingly required by regulatory agencies concerned with product leakage into the surrounding environment.
A significant number of liquid storage tanks now require retrofit systems for monitoring product leakage. The addition of an in-tank monitor usually requires excavation of an underground tank and addition of a dedicated riser pipe for the monitoring equipment. This results in disruption of business pertaining to the tank during the excavation procedure and concerns for the aesthetics of the surrounding property because excavation normally leaves significant scaring, as well as the possibility of a tank leak arising due to the disturbance involved in excavation.
A typical underground storage tank for liquids, such as gasoline and other oil-based products, is provided with a vertical cylindrical riser pipe used to accept product deliveries. A circular manhole surrounding it provides access to the riser for delivery purposes. A thin wall aluminum "drop tube" minimizes product evaporation during deliveries. The "drop tube" fits within the riser and extends into the tank to a location within several inches from the tank bottom.
It is not practical to simply hang a monitoring probe or other equipment vertically within the existing riser pipe for an underground liquid storage tank. Such placement of suspended equipment within a tank would interfere with the intended purpose of the riser pipe for product delivery needs. Positioning any substantial equipment directly under the riser pipe would also eliminate use of a drop tube, which is now required in the United States by statute.
To accommodate the need for a drop tube within a riser pipe and tank, it is necessary to suspend the hanger for in-tank equipment within the riser pipe closely adjacent to a side wall of the riser pipe, where it will not substantially interfere with placement of a drop tube. The drop tube can then be longitudinally creased to provide clearance for the hanger along the riser pipe.
Monitoring equipment, such as a probe, suspended by a hanger within the tank interior must also be transversely offset from an extension of the supporting riser pipe, so that it does not contact or interfere with the inserted drop tube. This transverse offset of the hanger requires use of a longitudinal rigid member extending through the riser pipe and capable of supporting an offset support for the probe.
In-tank liquid level probes using ultrasonic technology can be extremely accurate. In order to provide consistent readings of liquid level within the tank, it is vital that such probes be maintained in a fixed position with respect to the interior surfaces of the tank.
Early testing of hangers for this type of sensitive monitoring equipment showed degradation of results due to the thermal contraction and expansion of the supporting hanger structure within the riser itself. This was particularly a problem in installations where the risers extended above ground level.
The present invention has been designed to reference the elevation of the equipment relative to the interior of a tank while also isolating the position of the equipment within the tank from dimensional changes in the length of a rigid support member extending along the supporting riser pipe.
The present invention lends itself to retrofitting of underground storage tanks by using an existing riser pipe to suspend equipment, such as an ultrasonic liquid level monitor or probe, within the tank interior. It leaves the riser pipe fully accessible for its conventional purposes (such as product deliveries). The invention also can be applied to new tank installations, where a separate dedicated riser pipe can be provided on the tank without substantial additional expense or environmental disruption.